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Basic Atomic and Nuclear Physics
Published in Michael Ljungberg, Handbook of Nuclear Medicine and Molecular Imaging for Physicists, 2022
Gudrun Alm Carlsson, Michael Ljungberg
For a nucleus with mass number A greater than 150, another and more important form of dynamic instability will occur, called α-instability, leading to an α-decay where a helium nucleus 4He2+ will be emitted from the parent nucleus. This is possible because of the relatively high binding energy of the 4He nucleus. The emission of other lighter nuclei than the He is not energetically possible owing to the low binding energy of these potential candidates.
Radioactivity
Published in W. P. M. Mayles, A. E. Nahum, J.-C. Rosenwald, Handbook of Radiotherapy Physics, 2021
Excepting catastrophic events such as fusion or fission, more stable structures can be obtained through changes in the number or in the nature of nucleons for a given nucleus. For instance, a nucleus with an excess of neutrons can eject a negative charge, changing a neutron into a proton (β– emission), whereas a nucleus with an excess of protons can eject a positive charge, changing a proton into a neutron (β+ emission) – see Section 2.2.4. Very heavy nuclei that contain too many protons and neutrons can eject a group of two protons and two neutrons (i.e. a helium nucleus), which forms one of the most stable structures (α emission).
Non-FDG radionuclide imaging and targeted therapies
Published in Anju Sahdev, Sarah J. Vinnicombe, Husband & Reznek's Imaging in Oncology, 2020
Luigi Aloj, Ferdia A Gallagher
Recently, alpha emitters have been introduced in clinical practice, although applications are currently limited. These so-called high linear energy transfer (LET) emitters have the advantage of releasing a high-mass particle (a helium nucleus) which produces multiple ionizations in tissue with a short particle range (10–500 μm), resulting in significant radiation damage within the distance of a few cells from the site of decay, which can minimize normal tissue damage.
The intercellular communications mediating radiation-induced bystander effects and their relevance to environmental, occupational, and therapeutic exposures
Published in International Journal of Radiation Biology, 2023
Manuela Buonanno, Géraldine Gonon, Badri N. Pandey, Edouard I. Azzam
Quantification of health risks from occupational radiation exposures also concerns space exploration. During mission, only parts of the astronaut body are irradiated at any one time (Cucinotta et al. 1998), and radiation traversals are separated in both tissue location and time (Held 2009). It has been estimated that during transit beyond low Earth orbit, every cell nucleus within an astronaut’s body is traversed, on average, by an energetic proton every few days, by a helium nucleus once every few weeks, and by heavier high-charge particles (HZE) every few months (Cucinotta et al. 1998; Blakely 2000) while the rest of the cells would be bystanders. Besides highly localized energy deposition, HZE particles give rise to secondary radiation along the track due to heavy ion fragments and energetic electrons (i.e. δ rays). Whereas the radial spread of dose due to secondary heavy ion fragments extends up to 10–20 µm (Gonon et al. 2013), the range of δ rays can extend up to several cell diameters (Metting et al. 1988; Cucinotta et al. 1998). In cell cultures exposed to doses wherein a small fraction of the cells are targeted with HZE particles, markers of damage were increased in more cells than expected based on the number of cells traversed by HZE particles (Gonon et al. 2013). Using an insert co-culture system that allowed investigating HZE-particle-induced bystander effects in the absence of δ rays and secondary fragmentation products, bystander effects were shown to persist in progeny of bystander cells many generations after co-culture with HZE particle-irradiated cells (Buonanno, de Toledo, Azzam 2011; Buonanno, de Toledo, Pain, et al. 2011), and depended on the type of junctional channels that connected the irradiated donor cells with the bystander cells (de Toledo et al. 2017). The propagation of such detrimental effects was not observed in progeny of bystander cells present in cultures where less than 1% of the cells were exposed to microbeam protons, suggesting LET-dependence (Autsavapromporn et al. 2015). The possibility of increased risk of carcinogenesis caused by exposure to space radiation during prolonged space travel has been considered a limiting factor for human exploratory missions (National Research Council 2008). Work in mouse embryo fibroblasts has supported this premise by showing increased frequency of spontaneous neoplastic transformation in progeny of bystander cells from cultures exposed to densely ionizing radiations, including HZE or α particles (Buonanno, de Toledo, and Azzam 2011). Notably, gap junctional communication contributed to mediating the effect. Hence, whether in the case of residential radon or space exploration, studies of bystander effects have the potential to inform the available limited epidemiological surveys.